Send emails not to spam box !! (webmail issue)

1. Okay guys we have our site that sends hundreds of emails per day to our users (mass email) 2. Problem: The emails always get forwarded to the spam box, or trash section [login to view URL], [login to view URL], [login to view URL], [login to view URL], [login to view URL], [login to view URL], [login to view URL], etc. 3. Now when I use facebook, myspace, etc. It usually goes to a users inbox (not spam box) Solution: fix our script so that when a user gets their email, it goes directly to the inbox and not spam box. Our server specs: OS is Centos, Cpanel / whm, dedicated server